- A
Allow traffic from Outside to DMZ on port 443
This rule permits HTTPS traffic from the Internet (Outside) to the web server in the DMZ, which is the requirement.
- B
Allow traffic from DMZ to Outside on port 443
Why wrong: This rule permits outbound traffic from the DMZ to the Internet, which would allow the web server to initiate outbound connections, but does not allow inbound HTTPS requests.
- C
Allow traffic from Inside to DMZ on port 443
Why wrong: This rule permits internal corporate users to access the web server, but not external users from the Internet.
- D
Allow traffic from Outside to Inside on port 443
Why wrong: This would allow inbound traffic directly into the corporate network, bypassing the DMZ, which is not the intention and violates security best practices.
Quick Answer
The correct firewall rule is to allow traffic from the Outside interface to the DMZ interface on TCP port 443. This rule is necessary because HTTPS traffic originates from the internet and must be permitted to reach the web server in the DMZ, while the default implicit deny on the firewall would otherwise block all inbound connections. On the CompTIA Network+ N10-009 exam, this scenario tests your understanding of zone-based security and the principle of least privilege—the DMZ is intentionally isolated from the corporate Inside network, so the rule must specify the source as Outside and the destination as DMZ, not Inside. A common trap is confusing the source and destination interfaces or allowing traffic to the Inside zone, which would expose the internal network. Remember the memory tip: “Outside to DMZ on 443 keeps the web server open, but the inside stays secure.”
N10-009 Network Security Practice Question
This N10-009 practice question tests your understanding of network security. Read the scenario carefully and evaluate each option against the stated constraints before committing to an answer. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
A company wants to allow inbound HTTPS traffic to a web server located in the DMZ from the Internet. The firewall has three interfaces: Inside (corporate network), Outside (Internet), and DMZ (web server). Which of the following firewall rules is required?
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
Allow traffic from Outside to DMZ on port 443
The correct rule is to allow traffic from the Outside (Internet) interface to the DMZ interface on TCP port 443 (HTTPS). This permits inbound web requests to reach the web server while keeping the corporate Inside network isolated. The firewall must explicitly permit this traffic because the default implicit deny rule would otherwise block all inbound connections from the Outside zone.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
Allow traffic from Outside to DMZ on port 443
Why this is correct
This rule permits HTTPS traffic from the Internet (Outside) to the web server in the DMZ, which is the requirement.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
Allow traffic from DMZ to Outside on port 443
Why it's wrong here
This rule permits outbound traffic from the DMZ to the Internet, which would allow the web server to initiate outbound connections, but does not allow inbound HTTPS requests.
- ✗
Allow traffic from Inside to DMZ on port 443
Why it's wrong here
This rule permits internal corporate users to access the web server, but not external users from the Internet.
- ✗
Allow traffic from Outside to Inside on port 443
Why it's wrong here
This would allow inbound traffic directly into the corporate network, bypassing the DMZ, which is not the intention and violates security best practices.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often confuse the direction of the traffic flow, mistakenly thinking the rule should allow traffic from the DMZ to the Outside (Option B) because they focus on the server sending responses, rather than the client initiating the connection.
Detailed technical explanation
How to think about this question
In a three-legged firewall architecture, each interface belongs to a separate security zone, and traffic between zones must be explicitly permitted by stateful inspection rules. The firewall tracks connection state; for inbound HTTPS, the rule must match the initial SYN packet from Outside to DMZ, and the return traffic is automatically allowed by the state table. Real-world deployments often combine this rule with NAT (port forwarding) to map a public IP to the private DMZ server address.
KKey Concepts to Remember
- Read the scenario before looking for a memorised answer.
- Find the constraint that changes the correct option.
- Eliminate answers that are true in general but not in this case.
TExam Day Tips
- Watch for words such as best, first, most likely and least administrative effort.
- Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
How this comes up in practice
A security administrator must allow nursing staff to reach a patient records server while blocking access from the guest Wi-Fi VLAN. After applying an extended ACL, traffic is still blocked from nursing workstations. The ACL was applied outbound instead of inbound on the wrong interface. Questions like this test ACL direction and placement rules.
What to study next
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FAQ
Questions learners often ask
What does this N10-009 question test?
Network Security — This question tests Network Security — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Allow traffic from Outside to DMZ on port 443 — The correct rule is to allow traffic from the Outside (Internet) interface to the DMZ interface on TCP port 443 (HTTPS). This permits inbound web requests to reach the web server while keeping the corporate Inside network isolated. The firewall must explicitly permit this traffic because the default implicit deny rule would otherwise block all inbound connections from the Outside zone.
What should I do if I get this N10-009 question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Last reviewed: Jun 11, 2026
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